Jetting Apparatus and Method of Improving the Performance of a Jetting Apparatus

ABSTRACT

The present invention is generally related to a jetting device for jetting droplets of viscous medium onto a substrate, said jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which said droplets are jetted. In particular, the invention is related to a method, a measuring device, a jetting device, and a viscous medium container for use in such a jetting device for measuring or monitoring a level or volume of viscous medium during a jetting process and/or measuring electrical properties of the viscous medium to determine characteristics of the medium.

TECHNICAL FIELD

The present application refers to systems for applying viscous mediums onto substrates using jet printing within the field of electronics production. More specifically, the invention relates to a method of improving the performance of a jetting device, and a device for jetting droplets of viscous medium onto a substrate.

BACKGROUND

Systems, devices and methods for jetting droplets of viscous medium, e.g. solder paste or glue, onto a sub-strate, e.g. an electronic circuit board, are known in the art. See for instance patent publications U.S. Pat. No. 6,450,416 B1, US 2002/0043570 A1, US 2002/0047052 A1, US 2002/0014602 A1, US 2002/0015780 A1, US 2004/0118935 A1, US 2004/0217193 A1, US 2004/0262824 A1, US 2005/0092774 A1, US 2005/0167519 A1, WO 2005/048678, which are incorporated herein by reference.

In the MY500 Jet Printer provided by Mydata automation AB, a system for jetting viscous medium comprises a jet printing machine, a solder paste container for containing solder paste to be jetted, a residue receptacle for holding residue and surplus of solder paste resulting from the jetting process, an ejector element for performing the actual jetting of the solder paste, and a holder matable with the jet printing machine. The ejector comprises a feeder in the form of a feed screw, which is powered by a stepper motor arranged in the holder matable via interface means of the stepper motor and the ejector.

The throughput is an essential factor in the manufacturing of electronic circuit boards. This has lead to, inter alia, a desire of increasing the speed at which a substrate is provided with viscous medium and a desire to eliminate or, at least minimize, interruptions or breaks during the production process. A way to improve the throughput or manufacturing speed of electronic circuit boards is to eliminate or reduce the need for operator interventions due to, inter alia, interruptions in the jet printing process. Such interruptions may be caused by shortage of solder paste. Accordingly, it is of high importance for the production speed to obtain a reliable and accurate measure of the solder paste quantity remaining in the solder paste tube. Today, this may be performed by so called “dead counting”, i.e. the number of ejected droplets is counted. However, this is impaired with problems. For example, the accuracy is low due to counting errors caused by difficulties of estimating the quantity of solder paste in the droplets or due to the fact that information regarding the quantity of solder paste contained in the solder paste tube may be erroneous. An alternative way of measuring the solder paste level in a solder paste tube is to arrange inductive transducers or sensors at a predetermined level at the tube, which deliver a signal when the solder paste has reached the level that the solder paste is about to run out. This method is associated with drawbacks, for example, that the operator of the jetting device is not provided with any information regarding the solder paste quantity during a jet printing process until the solder paste is about to ran out.

In addition, the high quality requirements of the electronic industry and the detrimental consequences of errors appearing in circuit boards has led to an arising interest in means for monitoring and/or determining characteristic features or parameters of the solder paste, for example, with respect to quality including oxidation degree of the solder pellets, solder paste type, remaining shelf-life, etc. during a jet printing operation as well as before a jet printing operation is initiated when the solder paste tube is mounted in the jet printing device.

Hence, a need exists for improved jetting methods and devices.

Further, there is a need within the art of jet printing of improved and more reliable methods and devices for measuring and/or monitoring the solder paste consumption during a jet printing process.

SUMMARY OF THE INVENTION

Thus, an object of the present invention is to provide an improved jetting method and device.

Another object of the present invention is to improve the performance of a device for jetting droplets of viscous medium onto a substrate.

A further object of the present invention is to provide improved and more reliable methods and devices for measuring and/or monitoring the solder paste consumption during a jet printing process.

These and other objects are achieved according to the present invention by providing a method and an apparatus having the features defined in the independent claims. Preferred embodiments are defined in the dependent claims.

According to an aspect of the present invention, there is provided a method for a jetting device for jetting droplets of viscous medium onto a substrate, the jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which the droplets are jetted. The method comprises the steps of: generating at least one electromagnetic signal in a detachable viscous medium container mounted in the jetting device; measuring a response signal to the generated electromagnetic signal in the viscous medium container; and determining a level of viscous medium in the viscous medium container using the response signal.

According to a second aspect of the present invention, there is provided a measuring device for a jetting device for jetting droplets of viscous medium onto a substrate, the jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which the droplets are jetted. The measuring device comprises: a signal generating circuit adapted to generate an electromagnetic signal in a detachable viscous medium container mounted in the jetting device; and signal measuring circuit adapted to measure a response signal to the generated electromagnetic signal in the viscous medium container and signal processing circuit connected to the signal measuring circuit and being adapted to determine a level of viscous medium in the viscous medium container using the response signal.

According to third aspect of the present invention, there is provided a jetting device for jetting droplets of viscous medium onto a substrate, the jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which the droplets are jetted, the jetting device further comprising a measuring device in accordance with the second aspect of the present invention.

According to a fourth aspect of the present invention, there is provided a viscous medium container for holding a viscous medium adapted to attached in a jetting device for jetting droplets of the viscous medium onto a substrate, the jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which the droplets are jetted. The viscous medium container comprises: at least one first conducting element arranged at an inner wall of the container; at least one second conducting element arranged at an inner wall; the first conducting element and the second conducting element being connectable to a measuring device in accordance with the second aspect of the present invention.

According to a further aspect of the present invention, there is provided a computer program product, directly loadable into an internal memory of a measuring device, comprising software code portions for causing the measuring device to perform steps of the method in accordance with first aspect of the invention.

Hence, the present invention is based on the idea of utilizing electromagnetical signals and/or fields applied in the viscous medium container, e.g. a solder paste tube, measuring a response of the viscous medium to the applied signals and/or fields, and determining the present level, volume, or filling degree of the viscous medium in the container using this response. Thereby, it is possible to continuously monitor and measure the volume or level of viscous medium held by the container during a jet printing process. This can be used to keep a user updated of the current level of viscous medium and the remaining volume of viscous medium and, thus, the jet printing process be improved, for example, in that interruption of the process can be predicted and/or adapted to the product production flow.

For the purposes of this application, it is to be noted that the term “viscous medium” should be inter-preted as solder paste, flux, adhesive, conductive adhe-sive, or any other kind of medium used in connection with mounting components on a substrate, conductive ink, resistive paste, or the like; that the term “deposit” refers to a connected amount of viscous medium applied at a position on a substrate as a result of one or more jetted droplets; and that the term “substrate” should be interpreted as a printed circuit board (PCB), a substrate for ball grid arrays (BGA), chip scale packages (CSP), quad flat packages (QFP), wafers, flip-chips, or the like.

It is also to be noted that the term “jetting” should be interpreted as a non-contact dispensing process that utilizes a fluid jet to form and shoot droplets of a viscous medium from a jet nozzle onto a substrate, as compared to a contact dispensing process, such as “fluid wetting.

In the following description, embodiments of jetting systems and methods will be described which comprise a jetting machine, viscous medium ejectors, viscous medium containers, residue receptacles, and holders. The term “ejector” refers to the element for actuating the actual jetting of viscous medium droplets; “container” refers to the element in which viscous medium is stored before and supplied from during jetting and is in fluid communica-tion with the ejector; “receptacle” refers to a container for receiving and holding surplus or residue viscous medium, for instance surplus viscous medium transported from the outlet of the ejector by means of pressurized air; and “holder” refers to a holding frame having mechanical and electrical interface with the jetting machine and holds the ejector, container and receptacle, thus forming an aggregate unit or assembly in conjunction with the ejector, container and receptacle, which in the following description sometimes will be referred to as a “cassette”; and “jetting machine” refers to the framework into which the unit or assembly is mounted. The jetting machine comprises means for holding, positioning and providing trigger signals for the cassettes during the jetting operation, and also means for holding and transporting the substrates onto which viscous medium is to be applied. The jetting machine further comprises software and inspection means for controlling and monitoring the entire viscous medium application process. However, unless the interaction between the jetting machine and the other elements or the cassette is described, the term jetting machine or jetting apparatus will in the following often refer to the entire system, including the elements referred to above.

In one aspect of the invention, the volume of viscous medium held by the container can be measured by providing the plunger provided at the end of the container opposite an outlet end with magnetic properties. Then, the movement of the plunger within the container, indicative of the viscous medium volume and filling degree, can be monitored using external measuring equipment including the signal measuring circuit and the signal processing circuit. Arranging a permanent magnet in the plunger, for instance a ferrite magnet, can provide the magnetic properties. Alternatively, the plunger material could be a polymer filled with magnetic particles. Many types of non-contact measurement methods could be adapted to perform the task of measuring the viscous medium volume.

In one embodiment, an array of hall effect sensor is arranged in proximity to the container. The sensors detect the magnetic field generated by the magnetic plunger in the viscous medium and deliver a current at detection of a field. As the plunger moves within the container, indicative of a viscous medium volume and filling degree, only the sensors that detect a magnet field within the viscous medium will deliver the current. Thus, by combining signals from one or more of the sensors, the position of the plunger can be determined and thereby the level of the viscous medium in the container.

Furthermore, in other exemplifying embodiments for measuring the amount of viscous medium in the containers, the viscous medium containers per se are provided with conduction paths within the actual container. Thus, the conduction paths are essentially arranged to be in electrical contact with the viscous medium such that electrical properties of the medium can be measured. Thereby, measuring the impedance in the viscous medium content can monitor the amount or filling degree of the viscous medium contained in the container. A change in the impedance level, or in fact the DC component, can be calculated and converted into a corresponding change in the volume of viscous medium. It should be noted that the conduction paths within the container could be in the form of conduction points in contact with the viscous medium, while other or major portions of the conductions paths can be located in portions of the container where there is no contact with the viscous medium.

Also, the provision of conduction paths or points within the viscous medium container, provides the possibility to determine the permittivity, the loss factor or dielectric constant of the viscous medium through impedance measurements and other characteristics of the viscous medium, for example, with respect to quality, remaining shelf-life, etc, can be monitored. For instance, the viscous medium could have a limited useful life, i.e. that the quality of the viscous medium deteriorates over time due to, inter alia, oxidation of the solder particles in solder paste. Furthermore, by conducting impedance measurements over a predetermined frequency range it is possible to obtain a “fingerprint” of the viscous medium which may be used to identify a certain type of viscous medium, for example, a solder paste having a certain quality or produced by a certain manufacturer. It is thereby also possible to, for example, verify that a solder paste container actually contains the indicated solder paste.

In a further embodiment of the present invention, measurement probes are arranged in a passage between the container and an ejector chamber of the ejector element, for example, between the container and a feed screw essentially to be in electrical contact with the viscous medium such that electrical properties of the medium can be measured. This provides the possibility to monitor other characteristics of the viscous medium. This may be combined with the magnetic plunger to provide the possibility to monitor the volume, or level, of the viscous medium by means of the detection of the magnetic field in the container and the electrical properties of the viscous medium by means of the impedance measurements in the passage between the container and the ejector chamber.

According to a further embodiment, the plunger is made electrically conducting and may short-circuit conduction paths or points arranged in the container. Thereby, it is possible to determine the level of the viscous medium within the container. This may be combined with measurement probes arranged in passages between the container and the ejection chamber of the ejector element, for example, between the container and the feed screw or in the ejection chamber such that electrical properties of the medium and the level of the viscous medium within the container can be measured.

As realized by the person skilled in the art, steps of the methods of the present invention, as well as preferred embodiment thereof, are suitable to realize as a computer program or a computer readable medium.

The features that characterize the invention, both as to organization and to method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawings. It is to be expressly understood that the drawings is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES OF DRAWINGS

FIG. 1 is a perspective view showing the general outline of a machine for application of solder paste comprising a jetting device according to the present invention;

FIG. 2 is a general block diagram of the measuring device according to the present invention for measuring a level or volume of solder paste in a solder paste container and/or measure electrical properties of the solder paste to determine characteristics of the solder paste;

FIG. 3 is an embodiment of a viscous medium container according to the present invention;

FIG. 4 is an embodiment of a viscous medium container arranged in holder to be attached in a jetting apparatus according to the invention;

FIG. 5 is a schematic cross-sectional view of a solder paste container connected to a measuring device according to an embodiment of the present invention;

FIG. 6 is a schematic cross-sectional view of a solder paste container connected to a measuring device according to another embodiment of the present invention;

FIG. 7 is a schematic cross-sectional view of a solder paste according to a further embodiment of the present invention;

FIG. 8 is a schematic cross-sectional view of a solder paste container connected to a measuring device according to yet another embodiment of the present invention;

FIG. 9 is a perspective view a jetting apparatus according to the present invention connected to a work station; and

FIG. 10 is a schematic cross-sectional view of a solder paste container connected to a measuring device according to a further embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENT

FIG. 1 illustrates the general outline of a preferred embodiment of an apparatus 1 for providing a substrate 2 with deposits by dispensing droplets of a viscous medium onto the substrate 2, for example, jetting, in accordance with the present invention. For ease of description, the viscous medium will hereinafter be referred to as solder paste, which is one of the alternatives defined above. For the same reason, the substrate will be referred to as an electric circuit board and the gas will be referred to as air. In this embodiment, the jetting apparatus 1 is of a type comprising an X-beam 3 and an X-wagon 4, which is connected to the X-beam 3 via an X-rail and is movable in a reciprocating way along the X-rail. The X-beam, in turn, is movably connected to a Y-rail 17, the X-beam 3 thereby being movable to the X-rail 16. The Y-rail 17 is rigidly mounted in the jetting apparatus 1. Generally, the movements are provided by linear motors (not shown).

Furthermore, the jetting apparatus 1 comprises an internal conveyor 17 for carrying the board 2 through the jetting apparatus 1, and a locking device for locking the board 2 when jetting is to take place.

A docking device is attached to the X-wagon 4 for enabling releasable mounting of an assembly 5 at the docking device 8. The assembly 5 is arranged for dispensing droplets of solder paste, i.e. jetting, which impact and form deposits on the board 2. The jetting apparatus 1 also comprises a vision device, e.g. a camera 15. The camera 15 is used for determining the position and rotation of the board 2 and for checking the result of the dispensing process by viewing the deposits on the board 2.

Additionally, the jetting apparatus 1 comprises a vacuum ejector (not shown in FIG. 1) arranged on the X-wagon 4, and a source of compressed air (not shown). The vacuum ejector, as well as the source of compressed air, is in communication with the docking device 8 via air conduit interface means, which are connectable to com-plementary air conduit interface means, of the docking device.

As understood by those skilled in the art, the jetting apparatus comprises a control unit (not explicitly shown in FIG. 1) for executing software running the apparatus and for controlling functions of a measuring device according to the present invention.

Briefly, the jetting apparatus works as follows. The board 2 is fed into the jetting apparatus 1 by means of the conveyor 18, upon which the board 2 is placed. When the board 2 is in the correct position under the X-wagon 4, the board 2 is fixed with the aid of the locking device. By means of the camera, fiducially markers are located, which markers are prearranged on the surface of the board 2 and used to determine the precise position thereof. Then, by moving the X-wagon over the board 2 in a predetermined (pre-programmed) pattern and operating the jetting assembly 5 at predetermined locations, solder paste is applied on the board 2 at the desired locations.

In FIG. 2, a general block diagram of the measuring device 20 (which will be described in more detail with reference to FIGS. 3-8) according to the present invention for measuring a level or volume of solder paste in a solder paste container 21 attached in the jetting apparatus 1 and/or measure electrical properties of the solder paste to determine characteristics of the solder paste is shown.

The measuring device 20 comprises a signal generating circuit 22 adapted to generate an electromagnetic signal in a solder paste container 21 when attached in a container holder, see FIG. 4. Moreover, the measuring device 20 comprises a signal measuring circuit 23 adapted to measure response signals to the generated electromagnetic signal in solder paste container 21, which signal measuring circuit may include signal measuring sensors (see FIG. 5), and a signal processing circuit 24 connected to the signal measuring circuit 23 adapted to determine a level of solder paste in the container and/or characteristics such as electrical properties of the solder paste using the response signals. The measuring device 20 may be controlled of; a control unit (not shown) of the jetting apparatus 1. Alternatively, the measuring device 20 may include logic for executing measuring functions, which logic may be arranged in the circuits of the measuring device 20. Furthermore, the measuring device 20 includes a memory circuit 25, which memory circuit can be arranged in the circuits of the measuring device 20, for example, in the signal processing circuit 24. Alternatively, the memory circuit may be arranged in the control unit of the jetting apparatus 1. The memory circuit 25 may include a random access memory (RAM) and/or a non-volatile memory such as a read-only memory (ROM). For example, information related to the solder level paste measuring and solder paste characteristics can be stored in the memory circuit 25.

With reference to FIGS. 3 and 4, an embodiment of a viscous medium container, which for ease of description, hereinafter will be referred to as solder paste container will be discussed. In FIG. 3, a solder paste container 31 intended for use in a jetting system, e.g. the jetting apparatus shown in FIG. 1, comprises an outlet 32 for providing the viscous medium to an ejector, or the like. At the other end of the container, i.e. opposite the outlet end, a plunger 33 or membrane is provided. Thereby, the solder paste content in the container 31 is held between the plunger 33 at one end and the outlet 32 at the other end. Thus, a surface of the plunger 33 is in contact with the solder paste and the medium is held in a voidless condition. During the jetting of droplets, and the corresponding emptying of the container of solder paste, the plunger 33 is moved in a direction towards the outlet 32 such that the voidless condition may be maintained when the amount of solder paste held by the container 31 is decreased during the jetting process. In FIG. 4, the container 31 is shown mounted in a container holder 34, which is adapted for attachment in the jetting apparatus.

Now, an aspect of the present invention will be discussed with reference to FIG. 5 showing a schematic cross-sectional view of a solder paste container. A solder paste medium container 51 intended for use in a jetting system, e.g. the jetting apparatus shown in FIG. 1, is provided with a plunger 53 with magnetic properties that generates a magnetic field in the container 51. The volume of solder paste held by the container 51 can be measured by monitoring the movement of the plunger 53 within the container 51 which is indicative of the solder paste volume and filling degree, i.e. monitoring the change of the magnetic field by means of the signal measuring circuit 23 shown in FIG. 2. Arranging a permanent magnet in the plunger, for instance a ferrite magnet, can provide the magnetic properties. Alternatively, the plunger material could be a polymer filled with magnetic particles.

According to one embodiment of the present invention, the signal measuring circuit 23 comprises an array of hall effect sensor elements 54 arranged in proximity of the container 51. The sensor elements 54 are arranged according to a longitudinal line and are preferable mounted parallel with a longitudinal axis of the container 51. For example, the sensor array 54 may be arranged at the holder 34 shown in FIG. 4. Each sensor element 54 is connected to the signal processing circuit 24 including a combining circuit (not shown) adapted to combine currents from respective sensor element 54 to determine a position of the magnetic element 53 in solder paste container 51 and adapted to determine a level of solder paste in the container 51 using the position determination of the magnetic element 53.

With reference now to FIG. 6, another embodiment of the present invention will be described. A solder paste container 61 is provided with first and second conductive elements 62 a, 62 b at an inner wall of the container 61, which conductive elements 62 a, 62 b are connectable to signal generator 64 of the signal generating circuit 22, see FIG. 2, and a signal measuring circuit 65 and a signal processing circuit 66. In one embodiment, the solder paste container 61 is provided with the conductive elements, e.g. conductive strips, per se. The signal measuring circuit 65 comprises resistive elements 67 connected to an amplifier 68 and an analog-to-digital converter 69.

Thus, the conduction paths are essentially arranged to be in electrical contact with the viscous medium, e.g. solder paste, such that electrical properties of the medium can be measured. Thereby, the amount or filling degree of the viscous medium contained in the container can be monitored by measuring the impedance in the solder paste content. According to this embodiment, the signal generator 64 applies a current via the first conductive element 62 a and the resulting impedance is measured by the signal measuring circuit 65 via the second conductive element 62 b. A change in the DC-impedance level can be calculated and converted into a corresponding change in the volume of solder paste.

It should be noted that the conduction paths within the container could be in the form of conduction points in contact with the solder paste, while other or major portions of the conductions paths can be located in portions of the container where there is no contact with the viscous medium.

Also, the provision of conduction paths or points within the solder paste container, provides the possibility to monitor other characteristics of the solder paste by measuring the impedance and calculating electrical properties of the viscous medium, e.g. the solder paste. For instance, the solder paste could have a limited useful life, i.e. that the quality of the solder paste deteriorates over time. Then, conduction paths in the container can be used for determining electrical properties of the viscous medium that would be indicative of whether the solder paste has passed its best-before date. For instance, the permittivity, the loss factor or dielectric constant of the viscous medium can be determined through DC- and AC-impedance measurements, i.e. complex impedance measurements. The impedance measurement are conducted over a predetermined frequency range, for example, in a range of 0-1 MHz or in a range of 0-500 KHz.

In one embodiment, the signal generating circuit 64 includes a signal generator adapted to generate DC and/or AC current waveforms over a predetermined frequency range which are delivered into the solder paste via conducting elements arranged within the container 61. For example, voltages of in range of about 0.5-50 V at a frequency range of about 0-1 MHz can be used. In another embodiment, voltages of in range of about 10-20 V at a frequency range of about 0-500 KHz can be used.

In FIG. 7, an embodiment of the solder paste container provided with conducting points is shown. A first array of conducting points 72 a and a second array of conducting points 72 b are arranged at an inner wall of the solder paste container 71. The first and second arrays 72 a and 72 b are, as the conductive strips shown in FIG. 6, connectable to a signal generator of the signal generating circuit 22, see FIG. 2, and a signal measuring circuit and a signal processing circuit.

With reference now to FIG. 8, a further embodiment of the present invention will be discussed. A first and a second measurement probe 82 a and 82 b are arranged in a passage 83 between the container and the ejection chamber of the ejector element, for example, between the container and the feed screw of an ejector element 87 essentially to be in electrical contact with the solder paste such that electrical properties of the paste can be measured. Alternatively, the probes 82 a and 82 b may be arranged in the ejection chamber or in a passage between the feed screw and the ejection chamber.

The first and second measurement probes 82 a and 82 b are connected: to a signal generator 84 of the signal generating circuit 22, see FIG. 2, and a signal measuring circuit 85 and a signal processing circuit 86. The signal measuring circuit 85 comprises resistive elements 90 connected to an amplifier 88 and an analog-to-digital converter 89. According to this embodiment, the signal generator 84 applies a current via the first conductive element 82 a and the resulting impedance is measured by the signal measuring circuit 85 via the second conductive element 82 b. For example, voltages of in range of about 0.5-50 V at a frequency range of about 0-1 MHz can be used. In another embodiment, voltages of in range of about 10-20 V at a frequency range of about 0-500 KHz can be used.

This provides the possibility to monitor other characteristics of the solder paste such as the electrical properties of the solder paste by means of the complex impedance measurements in the passage between the container and the ejection chamber of the ejector element, for example, between the container and the feed screw. Furthermore, in order to determine or measure the level of solder paste in the container 81, a plunger 93 with magnetic properties that generates a magnetic field in the container 81 is provided. The volume of solder paste held by the container 81 can thus, as described above, be measured by monitoring the movement of the plunger 93 within the container 81 which is indicative of the solder paste volume and filling degree, i.e. monitoring the change of the magnetic field by means of the signal measuring circuit 85. Arranging a permanent magnet in the plunger, for instance a ferrite magnet, can provide the magnetic properties. Alternatively, the plunger material could be a polymer filled with magnetic particles. The signal measuring circuit 85 comprises an array of hall effect sensor elements 94 arranged in proximity of the container 81. The sensor elements 54 are arranged according to a longitudinal line and are preferable mounted parallel with a longitudinal axis of the container 81. For example, the sensor array 94 may be arranged at the holder 34 shown in FIG. 4. Each sensor element 94 is connected to the signal processing circuit 86 including a combining circuit (not shown) adapted to combine currents from respective sensor element 94 to determine a position of the magnetic element 93 in solder paste container 81 and adapted to determine a level of solder paste in the container 81 using the position determination of the magnetic element. Consequently, this embodiment provide the possibility to monitor both the volume, or level, of the solder paste in the solder paste container 81 by means of the detection of the magnetic field in the container 81 and characteristics of the solder paste such as the electrical properties, e.g. permittivity and dielectric constant, of the solder paste by means of the complex impedance measurements in the passage 83 between the container and the ejection chamber of the ejector element, for example, between the container and the feed screw.

In another embodiment of the present invention, the measurement probes are arranged in the passages between the container and the ejection chamber of the ejector element, for example, between the container and the feed screw for measuring electrical properties of the solder paste such as permittivity or dielectric constant and the container is provided with conduction paths as described above for measuring a DC-impedance level to determine the solder paste level in the container. The measurement device described with reference to FIG. 6 can be used with minor adaptations as the person skilled within the art easily realizes.

Thus, it is possible to monitor both the volume, or level, of the solder paste in the solder paste container by means of the detection of the DC-impedance level in the container and characteristics of the solder paste such as the electrical properties, e.g. permittivity and dielectric constant, of the solder paste by means of the complex impedance measurements in passage between the container and the ejection chamber of the ejector element, for example, between the container and the feed screw.

In FIG. 9, a jetting apparatus in accordance with the present invention, for example a jetting apparatus as shown in FIG. 1, including any one of the embodiments for measuring the level of solder paste and/or electrical properties of the solder paste in order to determine characteristics of the solder paste described above and an external work station connectable to the jetting apparatus is shown. The work station 102 is comprises a display screen or monitor 104 for presenting information for a user by means of a graphical user interface (GUI) such as a level or volume of viscous medium in the viscous medium container and characteristics of the viscous medium, and input devices 106, for example, a keyboard and a mouse, which enable a user to, for example, input information and commands. An operator of the jetting can thus be presented with information regarding, for example, a remaining amount of viscous medium, estimated time remaining at current jetting droplet ejection rate until the container in the jetting apparatus has to be replaced, etc. The external work station 102 may communicate with the jetting apparatus 1 via a physical connection such as, for example, an USB connection or wirelessly by means of a number of different technologies including short range communication links including BLUETOOTH, or other types of short-range wireless connections such as Infrared.

Referring now to FIG. 10, a further embodiment of the present invention will be discussed. A plunger 113 arranged in a solder paste container 111 is provided with first conductive elements 112 a and the container 111 is provided with a second conductive element 112 b at an inner wall of the container 111, which conductive elements 112 a, 112 b are connectable to signal generator 114 of the signal generating circuit 22, see FIG. 2, and a signal measuring circuit 115 and a signal processing circuit 116. In one embodiment, the solder paste container 111 is provided with the conductive element, e.g. conductive strips, per se. The signal measuring circuit 115 comprises resistive elements 117 connected to an amplifier 118 and an analog-to-digital converter 119.

Thus, the conductive elements are essentially arranged to be in electrical contact with the viscous medium, e.g. solder paste, such that electrical properties of the medium can be measured. Thereby, the amount or filling degree of the viscous medium contained in the container can be monitored by measuring the impedance in the solder paste content. According to this embodiment, the signal generator 114 applies a current via the first conductive element 112 a arranged in the plunger 113 and the resulting impedance is measured by the signal measuring circuit 115 via the second conductive element 112 b. A change in the DC-impedance level can be calculated and converted into a corresponding change in the volume of solder paste.

It should be noted that the conduction path within the container could be in the form of conduction points in contact with the solder paste, while other or major portions of the conductions path can be located in portions of the container where there is no contact with the viscous medium.

Also, the provision of conduction paths or points within the solder paste container, provides the possibility to monitor other characteristics of the solder paste by measuring the impedance and calculating electrical properties of the viscous medium, e.g. the solder paste. For instance, the solder paste could have a limited useful life, i.e. that the quality of the solder paste deteriorates over time. Then, conduction paths in the container can be used for determining electrical properties of the viscous medium that would be indicative of whether the solder paste has passed its best-before date. For instance, the permittivity, the loss factor or dielectric constant of the viscous medium can be determined through DC- and AC-impedance measurements, i.e. complex impedance measurements. The impedance measurement are conducted over a predetermined frequency range, for example, in a range of 0-1 MHz or in a range of 0-500 KHz.

As the person skilled within the easily realizes, there are a number of conceivable alternative embodiments, for example, the second conductive element 112 b may be arranged in a passage between the container 113 and the ejection chamber of the ejector element 87, for example, between the container and the feed screw of an ejector element 87.

In one embodiment, the signal generating circuit 64 includes a signal generator adapted to generate DC and/or AC current waveforms over a predetermined frequency range which are delivered into the solder paste via conducting elements arranged within the container 61. For example, voltages of in range of about 0.5-50 V at a frequency range of about 0-1 MHz can be used. In another embodiment, voltages of in range of about 10-20 V at a frequency range of about 0-500 KHz can be used.

The preceding specific embodiments are illustrative of the practice of the invention. It is to be understood, therefore, that other expedients known to those of skill in the art or disclosed herein may be employed without departing from the invention as defined by the appended claims. It is therefore understood that the invention may be practiced otherwise than is specifically described without departing from the scope of the present invention. 

1-33. (canceled)
 34. A method for a jetting device for jetting droplets of viscous medium onto a substrate, said jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which said droplets are jetted, said method comprising the steps of: generating at least one electromagnetic signal in a detachable viscous medium container mounted in said jetting device, wherein a magnetic element is provided in or adjacent to said viscous medium container such that a magnetic field is generated in said viscous medium container, said magnetic element being movable as a response of a change of quantity of said viscous medium in said viscous medium container; measuring a response signal to said generated electromagnetic signal in said viscous medium container including: detecting said generated magnetic field in said viscous medium container; and producing at least one signal being proportional to a present quantity of viscous medium in said viscous medium container; determining a level of viscous medium in said viscous medium container using said response signal; providing a first conductive element in a passage between said container and an ejector chamber of said ejector element such that said first conductive element is in contact with said viscous medium; providing a second conductive element in a passage between said container and an ejector chamber of said ejector element such that said second conductive element is in contact with said viscous medium; applying an electrical current between said at least one first conducting element and said at least one second conducting element; and measuring an impedance of the viscous medium in said passage between said container and said ejector chamber to the applied electrical current.
 35. A method for a jetting device for jetting droplets of viscous medium onto a substrate, said jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which said droplets are jetted, said method comprising the steps of: generating at least one electromagnetic signal in a detachable viscous medium container mounted in said jetting device, wherein a magnetic element is provided in or adjacent to said viscous medium container such that a magnetic field is generated in said viscous medium container, said magnetic element being movable as a response of a change of quantity of said viscous medium in said viscous medium container; measuring a response signal to said generated electromagnetic signal in said viscous medium container including: detecting said generated magnetic field in said viscous medium container; and producing at least one signal being proportional to a present quantity of viscous medium in said viscous medium container; determining a level of viscous medium in said viscous medium container using said response signal; providing at least one first conducting element in said viscous medium container; providing at least one second conducting element in said viscous medium container; applying an electrical current between said at least one first conducting element and said at least one second conducting element; and measuring an impedance of the viscous medium in said viscous medium container to the applied electrical current.
 36. The method according to claim 35, wherein the step of providing conducting elements in said viscous medium container comprises the steps of: arranging a first longitudinal conductive strip at an inner wall of said viscous medium container in a longitudinal direction; arranging a second longitudinal conductive strip at an inner wall of said viscous medium container in said longitudinal direction substantially parallel to said first conductive strip; connecting said first conductive strip to a signal generator and a signal processing unit; and connecting said second conductive strip to said signal generator.
 37. The method according to claim 35, wherein the step of providing conducting elements in said viscous medium container comprises the steps of: arranging a first array of conductive elements at an inner wall of said viscous medium container in a longitudinal direction, said elements of said first array being arranged in a line and electrically separated from each other; arranging a second array of conductive elements at an inner wall of said viscous medium container in said longitudinal direction substantially parallel with said first array, said elements of said second array being arranged in a line and electrically separated from each other; connecting said elements of said first array to a signal generator and a signal processing unit; and connecting said elements of said second array to said signal generator.
 38. The method according to claim 34, wherein the step of measuring a response signal comprises the steps of: detecting a hall effect caused by said generated magnetic field being proportional to a quantity of viscous medium in said viscous medium container; and producing at least one signal being proportional to a present quantity of viscous medium in said viscous medium container using said detected hall effect.
 39. The method according to claim 38, wherein said step of determining a level of viscous medium in said viscous medium container comprises the steps of: combining at least one signal from one or more of said hall effect sensors to determine a position of said magnetic element in said viscous medium container; and determining a level of viscous medium in said viscous medium container using said position determination of the magnetic element.
 40. The method according to claim 34, further comprising the step of arranging said magnetic element in a plunger arranged to be positioned in said viscous medium container and adapted to apply a press on said viscous medium of said viscous medium container during a jetting operation.
 41. The method according to claim 34, wherein said applied current comprises at least one current waveform including a DC component, wherein the step of determining a level of viscous medium in said viscous medium container comprises the steps of: measuring the resistive component of said impedance, said resistive component of said impedance being proportional to level of viscous medium in said viscous medium container; and determining the level of viscous medium in said viscous medium container using said resistive component.
 42. The method according to claim 34, wherein said applied current comprises at least one current waveform including an AC component, further comprising the steps of: measuring a reactive or a capacitive component of said impedance over a predetermined frequency range; determining a complex impedance using said resistive component and said reactive or capacitive component of said impedance; and using said complex impedance and/or said reactive or capacitive component of said impedance to determine characteristic features of said viscous medium.
 43. The method according to claim 34, further comprising the step of: determining electrical properties of said viscous medium, said electrical properties including permittivity, loss factor, or dielectric constant.
 44. The method according to claim 34, wherein said characteristic features includes a degree of oxidation of particles in said viscous medium, or content of lead.
 45. A measuring device for a jetting device for jetting droplets of viscous medium onto a substrate, said jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which said droplets are jetted, said measuring device comprising: signal generating circuit adapted to generate an electromagnetic signal in a detachable viscous medium container mounted in said jetting device, said signal generating circuit comprising a magnetic element adapted to be arranged in or adjacent to said viscous medium container and to generate a magnetic field in said viscous medium container, said magnetic element being movable as a response of a change of quantity of said viscous medium in said viscous medium container; signal measuring circuit adapted to measure a response signal to said generated electromagnetic signal in said viscous medium container, wherein said signal measuring circuit is adapted to: detect said generated magnetic field in said viscous medium container, and produce at least one signal being proportional to a present quantity of viscous medium in said viscous medium container; and a signal processing circuit connected to said signal measuring circuit and being adapted to determine a level of viscous medium in said viscous medium container using said response signal, said signal processing circuit being connectable to: at least one first conducting element arranged in a passage between said container and an ejector chamber of said ejector element; and at least one second conducting element arranged in said in a passage between said container and an ejector chamber of said ejector element; wherein said signal generating circuit is adapted to apply an electrical current between said at least one first conducting element and said at least one second conducting element; and wherein said signal measuring circuit including an impedance measuring circuit adapted to measure an impedance of the viscous medium in said passage between said container and said ejector chamber to the applied electrical current.
 46. A measuring device for a jetting device for jetting droplets of viscous medium onto a substrate, said jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which said droplets are jetted, said measuring device comprising: signal generating circuit adapted to generate an electromagnetic signal in a detachable viscous medium container mounted in said jetting device, said signal generating circuit comprising a magnetic element adapted to be arranged in or adjacent to said viscous medium container and to generate a magnetic field in said viscous medium container, said magnetic element being movable as a response of a change of quantity of said viscous medium in said viscous medium container; signal measuring circuit adapted to measure a response signal to said generated electromagnetic signal in said viscous medium container, wherein said signal measuring circuit is adapted to: detect said generated magnetic field in said viscous medium container, and produce at least one signal being proportional to a present quantity of viscous medium in said viscous medium container; and wherein said signal generating circuit further comprises a signal generator connectable to: at least one first conducting element adapted to be arranged in said viscous medium container; at least one second conducting element adapted to be arranged in said viscous medium container; wherein said signal generator is, when connected to said conductive elements, adapted to apply an electrical current between said at least one first conducting element and said at least one second conducting element; and wherein said signal measuring circuit includes an impedance measuring circuit adapted to measure an impedance of the viscous medium in said viscous medium container to the applied electrical current.
 47. The measuring device according to claim 46, wherein said at least one first conducting element is a first longitudinal conductive strip adapted to be arranged at an inner wall of said viscous medium container in a longitudinal direction and connected to said signal generator and said signal processing circuit; said at least one second conducting element is a second longitudinal conductive strip adapted to be arranged at an inner wall of said viscous medium container in said longitudinal direction substantially parallel to said first conductive strip and connected to said signal generator.
 48. The measuring device according to claim 46, wherein said at least one first conducting element is a first array of conductive elements adapted to be arranged at an inner wall of said viscous medium container in a longitudinal direction, said elements of said first array being arranged in a line and electrically separated from each other and connected to said signal generator and said signal processing circuit; said at least one second conducting element is a second array of conductive elements adapted to be arranged at an inner wall of said viscous medium container in said longitudinal direction substantially parallel to said first conductive array, said elements of said second array being arranged in a line and electrically separated from each other and connected to said signal generator.
 49. The measuring device according to claim 45, wherein said signal measuring circuit comprises an array of hall effect sensors adapted to be arranged in a longitudinal direction parallel with said viscous medium container, said hall effect sensors being adapted to: detect a hall effect caused by said generated magnetic field being proportional to a quantity of viscous medium in said viscous medium container; and produce at least one signal being proportional to a present quantity of viscous medium in said viscous medium container using said detected hall effect.
 50. The measuring device according to claim 49, wherein said signal processing circuit is adapted to: combine a signal from one or more of said hall effect sensors to determine a position of said magnetic element in said viscous medium container; and determine a level of viscous medium in said viscous medium container using said position determination of the magnetic element.
 51. The measuring device according to claim 45, wherein said magnetic element is arranged in a plunger arranged to be positioned in said viscous medium container and adapted to apply press on said viscous medium of said viscous medium container during a jetting operation.
 52. The measuring device according to claim 45, wherein said signal generator is adapted to apply an electrical current comprising at least one current waveform including a DC component; wherein said impedance measuring circuit is adapted to measure the resistive component of said impedance, said resistive component of said impedance being proportional to level of viscous medium in said viscous medium container; and wherein said signal processing circuit is adapted to determine the level of viscous medium in said viscous medium container using said resistive component.
 53. The measuring device according to claim 45, wherein said signal generator is adapted to apply an electrical current comprising at least one current waveform including an AC component; wherein said impedance measuring circuit is adapted to measure a reactive or a capacitive component of said impedance over a predetermined frequency range; wherein said impedance measuring circuit is adapted to determine a complex impedance using said resistive component and said reactive or capacitive component of said impedance; and wherein analyzing circuit connected to said impedance measuring circuit is adapted to use said complex impedance and/or said reactive or capacitive component of said impedance to determine characteristic features of said viscous medium.
 54. The measuring device according to claim 45, wherein said signal processing circuit is adapted to determine electrical properties of said viscous medium, said electrical properties including permittivity, loss factor, or dielectric constant.
 55. The measuring device according to claim 45, wherein said characteristic features includes a degree of oxidation of particles in said viscous medium, or content of lead.
 56. A jetting device for jetting droplets of viscous medium onto a substrate, said jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which said droplets are jetted, said jetting device further comprising a measuring device in accordance with claim
 45. 57. A viscous medium container for holding a viscous medium adapted to be attached in a jetting device for jetting droplets of said viscous medium onto a substrate, said jetting device comprising an ejector element for performing the jetting process and a jetting outlet through which said droplets are jetted, said viscous medium container comprising: at least one first conducting element arranged at an inner wall; at least one second conducting element arranged at an inner wall; and wherein said viscous medium container is adapted to comprise an electrically conducting plunger, which plunger is adapted to apply press on said viscous medium of said viscous medium container during a jetting operation, and wherein said plunger is arranged to short-circuit said at least one first conducting element and said at least one second conducting element; and wherein said at least one first conducting element and said at least one second conducting element is connectable to a signal processing circuit adapted to, at detection of current flowing between said at least one first conducting element and said at least one second conducting element, determine the level of viscous medium in said viscous medium container using a short-circuiting position of said plunger.
 58. The viscous medium container according to claim 57, wherein said at least one first conducting element is a first longitudinal conductive strip arranged at an inner wall of said viscous medium container in a longitudinal direction substantially parallel to said first conductive strip and connectable to said signal generator and said signal processing circuit; and said at least one second conducting element is a second longitudinal conductive strip arranged at an inner wall of said viscous medium container in said longitudinal direction and connectable to said signal generator.
 59. The viscous medium container according to claim 57, wherein said at least one first conducting element is a first array of conductive elements arranged at an inner wall of said viscous medium container in a longitudinal direction, said elements of said first array being arranged in a line and electrically separated from each other and connectable to said signal generator and said signal processing circuit; said at least one second conducting element is a second array of conductive elements arranged at an inner wall of said viscous medium container in said longitudinal direction substantially parallel to said first conductive array, said elements of said second array being arranged in a line and electrically separated from each other and connectable to said signal generator.
 60. A computer program product, directly loadable into an internal memory of a measuring device, comprising software code portions for causing said measuring device to perform steps in accordance with claim
 34. 